Packaging materials for daily necessaries, general merchandise, foods, tablet drugs, etc. are required to have various properties such as transparency, moisture resistance, heat-sealing properties, vacuum or pressure formability and twist-wrapping properties. However, use of only one kind of a resin cannot meet these requirements. Therefore, multi-layer laminates each comprising a sheet or a film of a certain resin and a sheet or a film of other resin with different properties have been widely employed. Also in the field of packaging materials, recycling of raw materials or incineration of the packaging materials has been recently paid much attention. From this viewpoint, polyolefin resins tend to be preferably employed as the packaging materials.
Of the polyolefin resins, cycloolefin resins are particularly suitable for the packaging materials, because they have excellent transparency, moisture resistance, vacuum or pressure formability and dead fold properties and they can be recycled or incinerated without any problem. However, since the cycloolefin resins are amorphous, they rapidly soften at temperatures close to their glass transition temperatures to cause lowering of elastic modulus and strength. Therefore, the molding conditions in the processes of heat-sealing, inflation and vacuum or pressure forming are restricted.
Meanwhile, the packaging materials used for packaging foods are desired to have low oxygen permeability because the objects packaged by the packaging materials easily deteriorate when they are brought into contact with oxygen of air. The cycloolefin resins have excellent properties as the packaging materials, e.g., high moldability and transparency. However, in the uses where high oxygen barrier properties are required, for example, in the uses for food-packaging, they are desired to be further improved in these properties.
Containers using thermoplastic resins are described in, for example, Japanese Patent Publication No. 104732/1994 and Japanese Patent Laid-Open Publication No. 1352/1984. These publications disclose laminating of an ethylene/vinyl alcohol copolymer (EVOH) and other thermoplastic resin, and the thermoplastic resins laminated together with the EVOH are, for example, polyesters such as PET and polyamides such as nylon. Japanese Patent Laid-Open Publication No. 293159/1993 discloses a container made of a laminate of a resin and EVOH, and the resin used herein is a hydrogenation product of a ring opening polymer of a cycloolefin.
It is an object of the present invention to provide a multi-layer laminate which has excellent formability, transparency, interlaminar bond properties, moisture resistance, flexibility, tearability, heat-sealing properties and dead fold properties and which is well-balanced between oxygen permeability and transparency. It is another object of the invention to provide a film, a sheet and a packaging material each of which is formed from the multi-layer laminate.